In recent years, lithium secondary batteries, nickel-hydride batteries, and other secondary batteries are growing in importance as vehicle-mounted power supplies and as power supplies for personal computers and mobile phones. In particular, since lithium secondary batteries (typically, lithium ion batteries) are lightweight and allow manufacturing of high energy density, they are expected to be preferably used as high-output power source, vehicle-mounted power supplies.
With such lithium secondary batteries, expansion and contraction occurs at plates (positive electrode and negative electrode) in an electrode body due to charge and discharge in other words, fluctuations in a state of charge (SOC)), temperature variations, and the like. When a distance between plates increases, since electron conductivity in a positive electrode active material layer and a negative electrode active material layer declines, internal resistance rises and battery performance deteriorates. Therefore, with an assembled battery in which a plurality of lithium secondary batteries are laminated, pressure is desirably applied to individual cells that constitute the assembled battery in order to prevent the distance between plates from increasing.
In a battery module (assembled battery) described in Patent Literature 1, a pair of end plates is installed on outermost sides (either end) of a group of cells aligned in a direction of lamination of the cells and the pair of end plates is tightened and fixed in a direction in which the end plates approach each other in order to apply pressure (load) to each cell. In other words, with a conventional assembled battery, appropriate pressure is applied to each cell by bringing the respective cells into pressure contact with each other so that a length of the aligned group of cells (hereinafter, also referred to as a “cell laminate”) becomes equal to a prescribed length.